The present invention relates to a base layer for a combined synthetic and natural turf, comprising:
a fabric formed by a plurality of mutually substantially parallel warp threads and a plurality of mutually substantially parallel weft threads intersecting the warp threads, said fabric comprising a plurality of apertures, and
a plurality of synthetic grass fibers connected at least partially to the fabric, at least one of the ends of each fiber protruding outside the fabric and forming a synthetic grass blade. Such a base layer is known, for instance from WO-A-9400639.
Up until a number of years ago a large number of sports were practiced on natural turf. Natural turf has the advantage that it is relatively soft and wounds and injuries are thereby seldom caused during falls, sliding tackles and the like. The great drawback of natural turf however is that it can deteriorate significantly in quality due to intensive use and/or weather conditions. What remains is a badly damaged field with large, bare (sand) surfaces which cannot be played on, or only with difficulty, and which have an unattractive appearance.
Synthetic grass surfaces have therefore already existed for a number of years, in particular for hockey, tennis and the like. Synthetic grass surfaces require less maintenance and withstand a more intensive use than natural turfs. However, the drawback of synthetic turf is that the frictional resistance is so high that wounds and/or injuries can be caused in the case of sliding tackles and undesired falls.
In the present application the terms xe2x80x9cgrass surfacexe2x80x9d and xe2x80x9cturfxe2x80x9d are used interchangeably.
Therefore a hybrid turf or combination turf has already been proposed in the above mentioned patent document WO-A-9400639, in which the advantages of both types of turf are combined. This combination turf is formed by a conventional synthetic grass surface constituting a base layer on which a layer of growth substrate is strewn. Grass seed is sown into this growth substrate, so that the crowns of the grass lay between the synthetic grass fibers and are protected thereby. The synthetic grass is formed by a backing and a great number of upright synthetic grass fibers connected therewith. The synthetic grass fibers are regularly spaced, and may be connected to the backing by tufting or weaving. The backing is perforated, so as to allow water and roots of the natural grass to pass therethrough. As backing a coarse woven material is for instance proposed, wherein apertures are formed between the warp and weft threads. It is further proposed to construct the backing from two layers, an apertured top layer carrying the synthetic fibers and a bottom layer stabilizing the top layer with the fibers and preventing the fibers from becoming unstuck during handling of the synthetic grass. The bottom layer may be made from a biodegradable material, so that this will gradually disappear after the turf has been laid, leaving only the perforated top layer with the synthetic grass fibers.
In this known combination turf the emphasis is mainly on the synthetic grass, and there is relatively little room for growing a robust natural grass turf. Furthermore, the cost of the known combination turf is relatively high.
It is therefore the object of the present invention to provide a combination turf comprising a relatively high percentage of natural grass and which may be constructed and laid for a relatively moderate cost. This is achieved according to the invention by making use for the combined synthetic and natural turf of a base layer as described above, in which the fiber ends forming the synthetic grass blades protrude from the fabric at location where the weft threads and the warp threads intersect. By forming the synthetic grass blades exclusively at the intersections of the warp and weft threads, and not at those locations where only warp threads or weft threads are present, a base layer is obtained in which there is relatively much room for arranging natural grass. Furthermore, since the synthetic grass fibers protrude from the fabric at the intersections of warp and weft threads, the loads are transmitted to the base layer at those locations where this is strongest. It is preferable to have the synthetic grass fibers woven into the fabric, whereby a very strong connection is formed.
The apertures in the base layer may be formed immediately during manufacture thereof by enlarged spaces between adjacent warp and/or weft threads, but it is also possible to form the apertures only during use of the base layer by decomposition of warp and/or weft threads made from a biodegradable material.
The above-described base layer may be arranged between two layers of growth substrate, with grass being sown in the top layer. Due to the apertures, which are present from the start or are created in the course of time by decay or decomposition of the biodegradable threads, the roots of the natural grass plants have the opportunity to grow through the base layer and to become anchored in the bottom layer of growth substrate and possibly also at least partially in the base layer. Optimal rooting hereby becomes possible while the additional strength of the remaining fabric threads and synthetic grass blades is still retained.
Alternatively, it is also possible to suffice with one layer of growth substrate which is arranged on the base layer placed on a foundation. The roots can then become anchored in the layer of growth substrate, the foundation and/or the base layer.
In particular, the present invention provides a base layer for a combined synthetic and natural turf, the base layer comprising: a fabric formed by a plurality of mutually substantially parallel warp threads and a plurality of mutually substantially parallel weft threads intersecting the warp threads, said fabric comprising a plurality of apertures, and a plurality of synthetic grass fibers connected at least partially to the fabric, at least one of the ends of each fiber protruding outside the fabric and forming a synthetic grass blade, characterized in that the apertures are formed by enlarged spaces between adjacent warp and/or weft threads, and the fiber ends forming the synthetic grass blades protrude from the fabric at location where the weft threads and the warp threads intersect. In another aspect, the invention provides such a base layer further characterized in that the synthetic grass fibers are woven into the fabric.
In other embodiments, the invention provides such base layers further characterized in that the apertures are formed during use of the base layer by warp and/or weft threads made from a biodegradable material. In other embodiments, such base layers (further characterized in that the fabric is formed by a plurality of series of non-biodegradable weft threads and a plurality of series of biodegradable weft threads alternating with these series and a plurality of series of non-biodegradable warp-threads intersecting the weft threads and a plurality of series of biodegradable warp threads alternating with these series, and in that the ends of the synthetic grass fibers protrude from the fabric at the intersections of these series of non-biodegradable warp threads and non-biodegradable weft threads) are provided by the invention. In related embodiments, the invention provides such base layers comprising biodegradable threads further characterized in that the biodegradable material is chosen from jute, sisal, coconut fiber, or biodegradable polymers.
In another aspect, the invention provides such base layers further characterized in that the artificial grass fibers are monofilament fibers. In other related aspects, the invention provides such base layers further characterized in that at least part of the synthetic grass fibers has at least one colour other than green, which, in some embodiments, may be furthered characterized in that the synthetic grass fibers having different colours form a pattern like lines of a sportsfield or a club logo.
Base layers noted previously as being provided by the invention, in some embodiments, may be further characterized in that at least part of the fabric is impregnated or coated with fertilizers. Similarly, base layers noted previously as being provided by the invention, in other related embodiments, may be furthered characterized in that at least part of the non biodegradable threads comprise melting threads.
In other embodiments, combined synthetic and natural turf, comprising a foundation, a base layer (noted previously as being provided by the invention) arranged thereon, and a layer of growth substrate in which grass plants may grow arranged on the base layer, is provided by the invention. In related embodiments, the invention provides such combined synthetic and natural turf further characterized in that the thickness of the layer of growth substrate on the base layer is chosen such that the synthetic grass blades of the base layer protrude thereabove. In related embodiments, the invention provides such combined synthetic and natural turf (the thickness of the layer of growth substrate on the base layer being chosen such that the synthetic grass blades of the base layer protrude, or do not protrude, thereabove) further characterized by a layer of growth substrate arranged between the foundation and the base layer. In other related embodiments, the invention also provides such combined synthetic and natural turf (a layer of growth substrate being arranged, or not being arranged, between the foundation and the base layer) further characterized in that the growth substrate consists of xe2x80x9cinfertile leaf mouldxe2x80x9d, a mixture of sand and an organic material, or top layer mixtures applied in natural grass turfs. In additional related embodiments, the invention also provides such combined synthetic and natural turf (a layer of growth substrate consisting of, or not consisting of, xe2x80x9cinfertile leaf mouldxe2x80x9d, a mixture of sand and an organic material, or top layer mixtures applied in natural grass turfs) further characterized in that the turf is used as sportsfield or as grass turf in gardens, playgrounds, (recreational) parks or golf courses.
In another aspect, the invention provides method for creating a combined turf as described in the preceding paragraph, comprising the steps of:
a. arranging a base layer as noted previously as being provided by the invention on a foundation;
b. arranging a layer of growth substrate and grass seeds sown therein over the base layer, in such manner that the synthetic grass blades rise at least partially above the layer of growth substrate,
c. causing the grass seed to germinate and raising grass plants, and
d. mowing the natural grass to a length which is greater than the length of the synthetic grass blades.
The invention further provides such method, further characterized in that prior to arranging the base layer on the foundation a layer of growth substrate is arranged thereon. In an additional aspect, the invention provides such method (a layer of growth substrate being arranged, or not being arranged, on the foundation prior to arranging the base layer on the foundation) furthered characterized in that the step of arranging a layer of growth substrate including grass seeds over the base layer comprises the intermediate steps of:
b1. at least partially working or strewing the growth substrate into the base layer,
b2. sowing the grass seed into the growth substrate, and
b3. arranging the remainder of the growth substrate over the grass seed.